LT6604-5_15 Datasheet, PDF (13/16 Pages) Linear Technology – Dual Very Low Noise, Differential Amplifier and 5MHz Lowpass Filter

LT6604-5
APPLICATIONS INFORMATION
Junction temperature, T_J, is calculated from the ambient
temperature, T_A, and power dissipation, P_D. The power
dissipation is the product of supply voltage, V_S, and total
supply current, I_S. Therefore, the junction temperature is
given by:
T_J = T_A + (P_D • θ_JA) = T_A + (V_S • I_S • θ_JA)
where the supply current, I_S, is a function of signal level,
load impedance, temperature and common mode volt-
ages. For a given supply voltage, the worst-case power
dissipation occurs when the differential input signal is
maximum, the common mode currents are maximum (see
the Applications Information section regarding Common
Mode DC Currents), the load impedance is small and
the ambient temperature is maximum. To compute the
junction temperature, measure the supply current under
these worst-case conditions, use 43°C/W as the package
thermal resistance, then apply the equation for T_J. For
example, using the circuit in Figure 3 with DC differential
input voltage of 250mV, a differential output voltage of 1V,
1k load resistance and an ambient temperature of 85°C,
the supply current (current into V⁺) measures 32.2mA per
channel. The resulting junction temperature is: T_J = T_A +
(P_D • θ_JA) = 85 + (5 • 2 • 0.0322 • 43) = 99°C. The thermal
resistance can be affected by the amount of copper on the
PCB that is connected to V^–. The thermal resistance of the
circuit can increase if the exposed pad is not connected
to a large ground plane with a number of vias.
TYPICAL APPLICATIONS
Dual, Matched, 5MHz Lowpass Filter
3V 0.1μF
R_IN
0.01μF
I_IN
R_IN
V_OCM
(1V-1.5V)
R_IN
0.01μF
Q_IN
R_IN
4
34
25
–
1/2
+
27
LT6604-5
6
2 ₊ – ₂₉
7
3V 0.1μF
12
8
17
–
1/2
+
19
LT6604-5
14
10 ₊ – ₂₁
24
Q_OUT
GAIN = ^806Ω
R_IN
I_OUT
5MHz Phase Distribution
(50 Units)
30
25
20
15
10
5
0
–134.5 –134 –133.5 –133 –132.5 –132
5MHz PHASE (DEG)
66045 TA02
66045fa
13